1. Field of the Invention
The present invention relates to a micro-electro-mechanical device which has a microstructure body and a semiconductor element over the same surface, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, research on a micro-mechanical system which is called a “MEMS” has been actively developed. “MEMS” (Micro-electro-mechanical system) is an acronym of a micro-electro-mechanical system, and is called a “micromachine” (a semiconductor device including a micromachine). “Micromachine” is not clearly defined now, however, generally means a micro-device in which “a movable microstructure body having a stereoscopic structure” and “an electronic circuit having a semiconductor element” are integrated using a semiconductor fine-processing technology. The microstructure body is different from the semiconductor element, and has a movable portion having a stereoscopic structure and is provided with space for operating the movable portion.
In the micromachine, the microstructure body can be controlled by the electronic circuit. Therefore, unlike a conventional device which is controlled by central processing using a computer, the micromachine may be constructed as an autonomous decentralized system: such a series of operations is performed that information obtained with a sensor is processed by the electronic circuit and action is taken through an actuator.
There have been many studies on such micromachines. As for the manufacturing process, for example, since it has been impossible to be compatible with wafer manufacturing or a plastic assembly facility, an improved MEMS wafer level package has been proposed (Reference 1: Japanese Patent Laid-open No. 2001-144117).
Further, there is a document on an electro-mechanical device called a “MEMS” (Reference 2: Japanese Patent Laid-open No. 2004-1201). As a starting material of a thin film, an amorphous material, a nanocrystalline material, a microcrystalline material, and a polycrystalline material have been cited, and as its material, silicon, germanium, silicon-germanium, an anisotropic conductive material, an anisotropic piezoelectric material, copper, aluminum, tantalum, and titanium have been described in Reference 2. Then, a thin-film amorphous silicon layer is formed on a surface of a glass substrate and crystallized. For providing good electrical properties, the crystallization is performed by controlling laser irradiation.
In addition, as for a technology of a step of etching a sacrifice layer for forming space, for example, there is a document on a manufacturing method of a a micro-electro-mechanical device in which a first sacrifice layer member and a second sacrifice layer member are formed of different resist materials (Reference 3: Japanese Patent Laid-open No. 2004-133281). In Reference 3, by using different resist materials, the baking temperature is changed so that sacrifice layer members with different etching rates are formed.
As described in Reference 1, a microstructure body which is a component of a micromachine is formed by a process for manufacturing a semiconductor element using a silicon wafer. In particular, in order to obtain a material having a thickness and/or a strength enough for forming the microstructure body, micromachines which have been used in practice have mainly used a silicon wafer.
In addition, in order to mass-produce micromachines each having a microstructure body, it is necessary to reduce manufacturing cost. As one means thereof, there can be a method of forming a microstructure body and a semiconductor element for controlling the microstructure body over the same substrate. However, when forming a microstructure body and a semiconductor element over the same substrate, a step which is different from a manufacturing process of a semiconductor element, such as etching of a sacrifice layer is required; therefore, the process becomes complicated. As described above, manufacturing processes of a microstructure body and a semiconductor element for controlling it are different from each other and as a result, the microstructure body or the semiconductor element may be destroyed to stop functioning. Thus in manufacturing micromachines which have been used in practice, the microstructure body and the semiconductor element have been formed by different processes respectively in many cases.